The provision of a trailer hitch dolly interposed between the towing vehicle and the towed trailer has hitherto greatly reduced heavy hitch loads on the rear of the vehicle where the trailer was previously coupled directly thereto. Where a coil spring supported the trailer hitch ball on the dolly, as in my U.S. Pat. No. 3,837,677 dated Sept. 24, 1974, a reduction in side sway resulted, but pitching or fore-and-aft rising and falling still occurred when the dolly encountered a bad bump and this motion was transmitted to the towing car in the form of a jerking motion back and forth. The coil spring necessarily possessed a higher spring rate than was desirable, yet it could not be lengthened sufficiently to reduce the spring rate satisfactorily within the space available on the dolly, since such reduction required an excessively long coil spring which would encounter the road surface if made long enough to adequately dampen the oscillation. The present invention provides a leaf spring of great length which has a low spring rate and its oscillations are additionally dampened by a shock absorber connected thereto, and guide rods are provided to guide the oscillations. This construction eliminates the pitching fore-and-aft which occurs when the dolly meets a serious road defect and likewise eliminates the action transmitted thereby to the towing car as a jerking motion back and forth.